For my website Google PageSpeed Insights recommends to change expiration values for some cacheable resources like .css, .js,.svg ,google api ,siteimprove .Is it feasible to set the expiration values for the above files? If yes,then what configuration will be required for that?
Enabling browser caching for these items is not something which normally relates directly to Sitecore as they are typically static files within your webroot, not served by Sitecore. This question How to configure static content cache per folder and extension in IIS7? should help you with configuring the folders in your webroot to have the correct cache headers.
Tip: these changes would be applied to the web.config file and I would suggest using web.config transforms to apply those changes to the web.config rather than modifying it directly.
Would like to inquire if there is any method to Enabling caching for certain files/folder in ASP.Net MVC3
The target files are some CSS and Jquery js files which are likely not to change for a long period.
Kind regards,
Configure the HTTP Expires Response Headers from IIS, it is very simple, just check Expire Web content
http://technet.microsoft.com/en-us/library/cc770661(v=ws.10).aspx
And yes, use bundling! It will generate unique hash, scripts and styles will be recached when any file changes in the bundle.
I checked my site with google page speed.
It said Specify an expiration for my resources.
Can anyone tell me how to leverage browser caching for blogger?
You cannot set custom expiration for resources served by Blogger - that part is already done for you by Google servers. Having said that, if you serve content from any third party domains (which you are), then you should look into enabling compression and caching on those hosts.
Of course, sometimes this will be out of your control - ex, third party widgets which you do not control directly.
You will have to set the expires header in your hosting settings. If you have hosted your website on Google App Engine (which is free) you can set the expires header in webapp-web.xml to 10 days.
<include path="/assets/**.css" expiration="10d" />
<include path="/assets/**.js" expiration="10d" />
I have gone through your site and have seen that you use blogger for articles, you can not set the expires header for blogger images and posts.
I have used Google's infrastructure to host my images, CSS and JS files. But if you want to improvise your pagespeed score on you custom JS files and CSS files, my blogger post can help you to host static content in Google. My blogs pagespeed score is around 94.
Disclaimer: I have authored the post mentioned in the link.
If you are hosting your CSS and JS files in some other hosting location, you should look for help to set the expires header in case you are using Apache web server to host.
If I understand correctly, a broswer caches images, JS files, etc. based on the file name. So there's a danger that if one such file is updated (on the server), the browser will use the cached copy instead.
A workaround for this problem is to rename all files (as part of the build), such that the file name includes an MD5 hash of it's contents, e.g.
foo.js -> foo_AS577688BC87654.js
me.png -> me_32126A88BC3456BB.png
However, in addition to renaming the files themselves, all references to these files must be changed. For exmaple a tag such as <img src="me.png"/> should be changed to <img src="me_32126A88BC3456BB.png"/>.
Obviously this can get pretty complicated, particularly when you consider that references to these files may be dynamically created within server-side code.
Of course, one solution is to completely disable caching on the browser (and any caches between the server and the browser) using HTTP headers. However, having no caching will create it's own set of problems.
Is there a better solution?
Thanks,
Don
The best solution seems to be to version filenames by appending the last-modified time.
You can do it this way: add a rewrite rule to your Apache configuration, like so:
RewriteRule ^(.+)\.(.+)\.(js|css|jpg|png|gif)$ $1.$3
This will redirect any "versioned" URL to the "normal" one. The idea is to keep your filenames the same, but to benefit from cache. The solution to append a parameter to the URL will not be optimal with some proxies that don't cache URLs with parameters.
Then, instead of writing:
<img src="image.png" />
Just call a PHP function:
<img src="<?php versionFile('image.png'); ?>" />
With versionFile() looking like this:
function versionFile($file){
$path = pathinfo($file);
$ver = '.'.filemtime($_SERVER['DOCUMENT_ROOT'].$file).'.';
echo $path['dirname'].'/'.str_replace('.', $ver, $path['basename']);
}
And that's it! The browser will ask for image.123456789.png, Apache will redirect this to image.png, so you will benefit from cache in all cases and won't have any out-of-date issue, while not having to bother with filename versioning.
You can see a detailed explanation of this technique here: http://particletree.com/notebook/automatically-version-your-css-and-javascript-files/
Why not just add a querystring "version" number and update the version each time?
foo.js -> foo.js?version=5
There still is a bit of work during the build to update the version numbers but filenames don't need to change.
Renaming your resources is the way to go, although we use a build number and embed that in to the file name instead of an MD5 hash
foo.js -> foo.123.js
as it means that all your resources can be renamed in a deterministic fashion and resolved at runtime.
We then use custom controls to generate links to resources at on page load based upon the build number which is stored in an app setting.
We followed a similar pattern to PJP, using Rails and Nginx.
We wanted user avatar images to be browser cached, but on an avatar's change we needed the cache to be invalidated ASAP.
We added a method to the avatar model to append a timestamp to the file name:
return "/images/#{sourcedir}/#{user.login}-#{self.updated_at.to_s(:flat_string)}.png"
In all places in the code where avatars were used, we referenced this method rather than an URL. In the Nginx configuration, we added this rewrite:
rewrite "^/images/avatars/(.+)-[\d]{12}.png" /images/avatars/$1.png;
rewrite "^/images/small-avatars/(.+)-[\d]{12}.png" /images/small-avatars/$1.png;
This meant if a file changed, its URL in the HTML changed, so the user's browser made a new request for the file. When the request reached Nginx, it got rewritten to the simple name of the file.
I would suggest using caching by ETags in this situation, see http://en.wikipedia.org/wiki/HTTP_ETag. You can then use the hash as the etag. A request will still be submitted for each resource, but the browser will only download items that have changed since last download.
Read up on your web server / platform docs on how to use etags properly, most decent platforms have built-in support.
Most modern browsers check the if-modified-since header whenever a cacheable resource is in a HTTP request. However, not all browsers support the if-modified-since header.
There are three ways to "force" the browser to load a cached resource.
Option 1 Create a query string with a version#. src="script.js?ver=21". The downside is many proxy servers wont cache a resource with query strings. It also requires site-wide updating for changes.
Option 2 Create a naming system for your files src="script083010.js". However the downside to option 1 is that this as well requires site-wide updates whenever a file changes.
Option 3 Perhaps the most elegant solution, simply set up the caching headers: last-modified and expires in your server. The main downside to this is users may have to recache resources because they expired yet never changed. Additionally, the last-modified header does not work well when content is being served from multiple servers.
Here a few resources to check out: Yahoo Google AskApache.com
This is really only an issue if your web server sets a far-future "Expires" header (setting something like ExpiresDefault "access plus 10 years" in your Apache config). Otherwise, a browser will make a conditional GET, based on the modified time and/or the Etag. You can verify what is happening on your site by using a web proxy or an extension like Firebug (on the Net panel). Your question doesn't mention how your web server is configured, and what headers it is sending with static files.
If you're not setting a far-future Expires header, there's nothing special you need to do. Your web server will usually handle conditional GETs for static files based on last modified time just fine. If you are setting a far-future Expires header then yes, you need to add some sort of version to the file name like your question and the other answers have mentioned already.
I have also been thinking about this for a site I support where it would be a big job to change all references. I have two ideas:
1.
Set distant cache expiry headers and apply the changes you suggest for the most commonly downloaded files. For other files set the headers so they expire after a very short time - eg. 10 minutes. Then if you have a 10 minute downtime when updating the application, caches will be refreshed by the time users go to the site. General site navigation should be improved as the files will only need downloading every 10 minutes not every click.
2.
Each time a new version of the application is deployed to a different context that contains the version number. eg. www.site.com/app_2_6_0/ I'm not really sure about this as users bookmarks would be broken on each update.
I believe that a combination of solutions works best:
Setting cache expiry dates for each type of resource (image, page, etc) appropreatly for that resource, for example:
Your static "About", "Contact" etc pages probably arn't going to change more than a few time a year, so you could easily put a cache time of a month on these pages.
Images used in these pages could have eternal cache times, as you are more likey to replace an image then to change one.
Avatar images might have an expiry time of a day.
Some resources need modified dates in their names. For example avatars, generated images, and the like.
Some things should never be caches, new pages, user content etc. In these cases you should cache on the server, but never on the client side.
In the end you need to carfully consider each type of resource to determine what cache time to instruct the browser to use, and always be conservitive if you are unsure. You can increase the time later, but it's much more pain to uncache something.
You might want to check out the approach taken by the grails "uiperformance" plugin, which you can find here. It does a lot of the things you mention, but automates them (set expiry time to a long time, then increments version numbers when files change).
So if you're using grails, you get this stuff for free. If you are not - maybe you can borrow the techniques employed.
Also - borrowed form the ui-performance page, - read the following 14 rules.
ETags seemingly provide a solution for this...
As per http://httpd.apache.org/docs/2.0/mod/core.html#fileetag, we can set the browser to generate ETags on file-size (instead of time/inode/etc). This generation should be constant across multiple server deployments.
Just enable it in (/etc/apache2/apache2.conf)
FileETag Size
& you should be good!
That way, you can simply reference your images as <img src='/path/to/foo.png' /> and still use all the goodness of HTTP caching.
I haven't had a huge opportunity to research the subject but I figure I'll just ask the question and see if we can create a knowledge base on the subject here.
1) Using subdomains will force a client side cache, is this by default or is there an easy way for a client to disable it? More curious about what kind of a percentage of users I should be expecting to affect.
2) What all will be cached? Images? Stylesheets? Flash SWFs? Javascripts? Everything?
3) I remember reading that you must use a subdomain or www in your URL for this to work, is this correct? (and does this mean SO won't allow it?)
I plan on integrating this onto all of my websites eventually but first I am going to try to do it for a network of flash game websites so I am thinking www.example.com for the website will remain the same but instead of using www.example.com/images, www.example.com/stylesheets, www.example.com/javascript, & www.example.com/swfs I will just create subdomains that point to them (img.example.com, css.example.com, js.example.com & swf.example.com respectively) -- is this the best course of action?
Using subdomains for content elements isn't so much to force caching, but to trick a browser into opening more connections than it might otherwise do. This can speed up page load time.
Caching of those elements is entirely down the HTTP headers delivered with that content.
For static files like CSS, JS etc, a server will typically tell the client when the file was modified, which allows a browser to ask for the file "If-Modified-Since" that timestamp. Specifics of how to improve on this by adding some extra caching headers would depend on which webserver you use. For example, with Apache you can use the mod_expires module to set the Expires header, or the Header directive to output other types of cache control headers.
As an example, if you had a subdirectory with your css files in, and wanted to ensure they were cached for at least an hour, you could place a .htaccess in that directory with these contents
ExpiresActive On
ExpiresDefault "access plus 1 hours"
Check out YSlow's documentation. YSlow is a plugin for Firebug, the amazing Firefox web development plugin. There is lots of good info on a number of ways to speed up your page loads, one of which is using one or more subdomains to encourage the browser to do more parallel object loads.
One thing I've done on two Django sites is to use a custom template tag to create pseudo-paths to images, css, etc. The path contains the time-last-modified as a pseudo directory. This path component is stripped out by an Apache .htaccess mod_rewrite rule. The object is then given a 10 year time-to-live (ExpiresDefault "now plus 10 years") so the browser will only load it once. If the object changes, the pseudo path changes and the browser will fetch the updated object.